JP2005083522A - Ball screw device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrain the degree of freedom of a ball in the vicinity of a ball scooping portion to prevent peeling or wear on a screw shaft or a nut, and to reduce vibration and noise.
A screw shaft 12 having a screw groove 11 on an outer peripheral surface, a nut 14 having a screw groove 13 corresponding to the screw groove 11 on an inner peripheral surface and screwed onto the screw shaft 12, and both screw grooves Ends are fitted into holes 20 formed in the outer peripheral portion of the nut 14 so as to endlessly circulate the balls 15 rollingly loaded in the load region between 11 and 13 and the balls 15 rolling in the load region. In a ball screw device having a substantially U-shaped side cap 17 to be joined, a cushioning material 30 that is more flexible than the material of the screw shaft 12 from the ball scooping point to the load region between both screw grooves 11 and 13 is provided on the nut 14 side. The ball 15 is disposed on the restraining surface of the ball 15.
[Selection] Figure 1

Description

  The present invention relates to a ball screw device used in various industrial machines.

As a conventional ball screw device of this type, for example, as shown in FIG. 5, a tube circulation type ball screw device is known. In this ball screw device 1, a nut 6 having a helical thread groove 4 corresponding to the screw groove 2 is screwed onto a screw shaft 3 having a helical thread groove 2 on the outer peripheral surface.
The screw groove 4 of the nut 6 and the screw groove 2 of the screw shaft 3 are opposed to each other to form a spiral load region between them, and a large number of balls 5 as rolling elements are rolled in the load region. It is loaded movably. The nut 6 (or the screw shaft 3) is moved in the axial direction through the rolling of the ball 5 by the rotation of the screw shaft 3 (or the nut 6).
Further, a part of the outer peripheral surface of the nut 6 is a flat surface, and a set of two holes 7 communicating with the screw grooves 2 and 4 are formed on the flat surface so as to straddle the screw shaft 3. By fitting both ends of a substantially U-shaped circulation tube 8 as an example of a ball circulation member into a set of holes 7, the ball 5 revolving along the load region between both screw grooves 2, 4 is placed in the load region. In the middle of this, the circulation tube 8 is scooped up and returned to the original load trajectory, whereby the ball 5 is infinitely circulated.

By the way, in the conventional ball screw device, there is a connecting portion region B1 between the end region A1 of the circulation tube 8 and the load region C1 between the screw grooves 2 and 4. Further, in the circulation paths A1 and B1 other than the load region C1 between the screw grooves 2 and 4, the ball 5 circulates with a certain amount of clearance (path diameter−ball diameter) between the paths.
The amount of this clearance is such that the screw shaft 3, nut 6, and circulation tube 8 are in the vicinity of the ball scooping point (present in the B1 region) where the ball 5 is separated from the thread groove 2 of the screw shaft 3 toward the end of the circulation tube 8. The relative positional relationship differs from the gap amount in the circulation tube 8.
With reference to FIG. 6, the process in which the ball | bowl 5 returns to the load area | region C1 between both the thread grooves 2 and 4 through the inside of the circulation tube 8 is demonstrated.

As shown in FIG. 6, the ball 5 moves from the end region A1 of the circulation tube 8 to the load region C1 between the two screw grooves 2 and 4 serving as a ball screw device through the region B1 of the connecting portion.
In the end region of the circulation tube 8 of A1, the ball 5 is in the metal circulation tube 8 and does not contact the screw shaft 3. The inner diameter of the circulation tube 8 is about 3 to 10% larger than the diameter of the ball 5, and therefore the ball 5 moves in the circulation tube 8 with a certain degree of freedom (vibration). Next, in the region of the connecting portion of B1, the ball 5 may come into contact with the screw shaft 3, and the ball 5 moves with a gap between the path 5 and the path. Finally, in the load region of C1, the ball 5 is restrained and rolled between the two screw grooves 2 and 4, and there is no complete gap between the ball 5 and the two screw grooves 2 and 4.

  Since the region B1 of the connecting portion is present, the inner surface of the hole 7 of the nut 6 and the surface of the screw shaft 3 are all made of metal. The ball 5 moves. For this reason, peeling and wear are likely to occur at the land portion of the screw shaft 3 and the corner portion of the nut 6 in the B1 region and the C1 region (see FIG. 7), and it may cause noise and vibration.

For this reason, in the past, chamfering was applied to parts where there was a possibility of hitting the ball to reduce stress concentration, and as a measure to prevent peeling wear and noise, this would strictly control the shape of the chamfer. The problem of having to do arises.
The present invention has been made to eliminate such inconveniences, and restrains the degree of freedom of the ball in the vicinity of the ball scooping portion to prevent the screw shaft and nut from being peeled off and worn, An object of the present invention is to provide a ball screw device with excellent durability capable of reducing vibration and noise.

In order to achieve the above object, the invention according to claim 1 has a screw shaft having a spiral thread groove on the outer peripheral surface and a spiral screw groove corresponding to the screw groove of the screw shaft on the inner peripheral surface. A nut that is screwed onto the screw shaft, a large number of balls that are slidably loaded in a load region between the screw grooves, and the nut that allows the balls rolling in the load region to circulate infinitely. A ball screw device comprising a substantially U-shaped ball circulation member whose end is fitted in a hole formed in the outer peripheral portion of the screw shaft, wherein the ball extends from the screw groove of the screw shaft to the ball circulation member side. A cushioning material, which is softer than the material of the screw shaft, is disposed on the restraining surface of the ball on the nut side from the point of picking up the ball to the load region between the screw grooves.
According to a second aspect of the present invention, in the first aspect, the ball circulation member has leg portions fitted to the holes of the nut at both ends, and a passage for returning the ball and a return passage in each leg portion. Are side caps made of synthetic resin that are inclined with respect to the outer peripheral surface of the leg portion, and a part of the leg portion is used as the cushioning material.

According to the first aspect of the present invention, when the ball moves from the end region of the ball circulation member to the load region between the two screw grooves serving as the ball screw device through the region of the connection portion, Since a cushioning material that is more flexible than the material of the screw shaft is placed in the path on the nut side of the region, the ball absorbs the kinetic energy when it hits the flexible cushioning material, and the vibration is attenuated, so the degree of freedom of the ball It is restrained and moves to the load region between both screw grooves in this state.
As a result, it is possible to provide a ball screw device with excellent durability that can prevent the screw shaft and nut from being peeled off and worn near the ball scooping portion and can reduce vibration and noise.
In the invention of claim 2, in addition to the invention of claim 1, by using a part of the leg portion of the side cap made of synthetic resin as a cushioning material, the number of parts can be reduced and the cushioning material and the side cap can be reduced. The joints can be eliminated.

Hereinafter, an example of an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view of a main part for explaining a ball screw device as an example of an embodiment of the present invention, and FIG. 2 explains a process in which a ball passes through a side cap and returns to a load region between both screw grooves. FIG. 3 and FIG. 4 are sectional views for explaining a main part of a ball screw device according to another embodiment of the present invention.
As shown in FIG. 1, a ball screw device 10 which is an example of an embodiment of the present invention includes a screw shaft 12 having a spiral thread groove 11 on an outer peripheral surface and a spiral corresponding to the screw groove 11 on an inner peripheral surface. A nut 14 having a threaded groove 13 is fitted, and the threaded groove 13 of the nut 14 and the threaded groove 11 of the screw shaft 12 face each other to form a spiral load region therebetween. .

A large number of balls 15 as rolling elements are loaded in the load region so as to be able to roll, and the nut 14 (or screw shaft 12) rolls the ball 15 by rotation of the screw shaft 12 (or nut 14). It moves in the axial direction.
A flat surface is formed on a part of the outer peripheral surface of the nut 14, and the flat surface is configured by, for example, joining point-symmetric members divided into two along the axial direction to each other at the divided surfaces. The synthetic resin side cap 17 is fixed by a fixing means such as a screw.

The side cap 17 includes a cap body 17a and a pair of leg portions 19 such as a columnar shape or a block shape provided on the lower surface side of the cap body 17a and extending in a direction perpendicular to the axial direction of the screw shaft 12. The pair of leg portions 19 are spaced apart from each other in the axial direction of the screw shaft 12 and spaced from each other in the radial direction of the screw shaft 12.
These leg portions 19 are connected to a load region between the screw grooves 11 and 13 and are fitted into a pair of long holes 20 that are perforated on the flat surface of the nut 14. In the combined state, the cap body 17a is fixed to the nut 14 by fixing means such as screws. In this embodiment, the hole 20 drilled in the flat surface of the nut 14 is formed with its longitudinal direction directed in the lead angle direction of the screw grooves 11 and 13.

Further, inside each leg portion 19 of the side cap 17, there is a ball scooping (or ball returning) passage 21 extending in a direction tangential to the screw shaft 12 and in a direction substantially coinciding with the lead angle of both the screw grooves 11 and 13. A ball passage 22 is formed in the cap body 17a to connect the ball scooping passages 21 to each other.
These ball scooping passages 21 and ball passages 22 scoop up the balls 15 that roll on one (or the other) load area in the axial direction between the screw grooves 11 and 13 and pick up the other in the axial direction (or On the other hand, a ball circulation path for returning to the load region is formed in the side cap 17.

The side cap type ball screw device 10 is different from the conventional circulation tube type ball screw device in that the pair of leg portions 19 are simply fitted into the holes 20 formed in the flat surface of the nut 14 with almost no gap while This is because the direction of the ball scooping passage 21 formed inside the portion 19 can be inclined with respect to the outer peripheral surface of the leg portion 19.
For this reason, a hole 20 is formed in the flat surface of the nut 14 in a direction perpendicular to the screw shaft 12 as in a conventional circulation tube type ball screw device, and the side cap 17 is simply formed in the hole 20. While the structure in which the leg 19 is fitted, the traveling direction of the ball 15 in the ball scooping passage 21 formed in the leg 19 is tangential to the screw shaft 12 and coincides with the lead angle of both screw grooves 11 and 13. The nut 14 can be easily processed, and the design freedom of the scooping passage and the return passage of the ball 15 can be improved.

Here, in this embodiment, the portion on the nut 14 side of the leg portion 19 of the side cap 17 is extended by one ball from the designed ball scooping point to the load region C2 side between the screw grooves 11 and 13. Thus, a part of the leg portion 19 is used as a cushioning material 30 that is more flexible than the material of the screw shaft 12, and the cushioning material 30 is disposed on the restraint surface of the ball 15 on the nut 14 side.
As a result, as shown in FIG. 2, the ball 15 passes through the region A2 of the leg portion 19 at the end of the side cap 17 and passes through the region B2 of the connecting portion. When moving to the load region C2, the shock absorbing material 30 that is softer than the material of the screw shaft 12 is disposed in the path on the nut 14 side of the connecting region B2, so that the ball 15 hits the soft shock absorbing material 30. Then, the kinetic energy is absorbed and the vibration is attenuated, so that the degree of freedom of the ball 15 is restricted, and in this state, the ball 15 moves to the load region C2 between the screw grooves 11 and 13.

As a result, it is possible to prevent the screw shaft 12 and the nut 14 from being peeled or worn near the ball scooping portion, and to provide a ball screw device with excellent durability that can reduce vibration and noise. it can.
Moreover, since a part of the leg portion 19 of the side cap 17 is made of the cushioning material 30, the number of parts can be reduced and the joint between the region A2 and the region B2 can be eliminated.
Since the side cap 17 is a molded product made of a synthetic resin, there is a degree of design freedom. Therefore, referring to FIG. 2, the restraining surface of the ball 15 on the nut 14 side of the leg portion 19 in the B2 region. By reducing the clearance between the ball 15 and the path stepwise, the step between the load region C2 and the thread groove 13 of the nut 14 can be reduced, and the leg portion in the B2 region can be reduced. The ball 15 sandwiched between the restraining surface of the ball 15 on the side of the nut 14 and the screw groove 11 of the screw shaft 12 may be in a preload state.

  Further, the cushioning material 30 provided on the leg portion 19 of the side cap 17 is disposed along the spiral of the screw groove 11 of the screw shaft 12. In this case, the center of the ball 15 passes through the ideal spiral. . Further, if the hole 20 on the nut 14 side is a long hole that is long in the spiral direction of the screw groove 13 of the nut 14, the range of the cushioning material 30 can be increased. In this case, since the shock absorbing material 30 cannot receive a load as a ball screw device, it is desirable that the buffer material 30 has a length of two or less of the diameter of the ball 15 in the spiral direction in order to secure a load capacity as the ball screw device.

In addition, this invention is not limited to the said embodiment, In the range which does not deviate from the summary of this invention, it can change suitably.
For example, in the above-described embodiment, the side cap is taken as an example of the ball circulation member. However, the present invention is not limited to this, and the present embodiment is not limited to this case when the circulation tube 8 is used as the ball circulation member as shown in FIGS. The invention may be applied. 3 and 4, the reference numerals of the ball screw device already described in FIG. 5 are used. FIG. 3 shows an example with a scooping angle, and FIG. 4 shows a case of tangential scooping. In any case, the cushioning material 30 that is softer than the material of the screw shaft 3 is disposed on the restraining surface of the ball 5 on the nut 6 side from the ball scooping point to the load region C1 between the screw grooves 2 and 4. The effect similar to a form can be acquired.

It is principal part sectional drawing for demonstrating the ball screw apparatus which is an example of embodiment of this invention. It is explanatory drawing for demonstrating the process in which a ball | bowl passes through the inside of a side cap and returns to the load area | region between both screw grooves. It is principal part sectional drawing for demonstrating the ball screw apparatus which is other embodiment of this invention. It is principal part sectional drawing for demonstrating the ball screw apparatus which is other embodiment of this invention. It is principal part sectional drawing for demonstrating the conventional ball screw apparatus. It is explanatory drawing for demonstrating the process in which a ball | bowl passes through the inside of a circulation tube and returns to the load area | region between both screw grooves. It is explanatory drawing for demonstrating peeling and abrasion of the land part of a screw shaft.

Explanation of symbols

10 Ball Screw Device 11 Screw Groove 12 Screw Shaft 13 Screw Groove 14 Nut 15 Ball 17 Side Cap (Ball Circulating Member)
19 leg 20 hole 21 ball scooping passage 30 cushioning material

Claims (2)

A screw shaft having a spiral thread groove on the outer peripheral surface, a nut having a spiral thread groove corresponding to the screw groove of the screw shaft on the inner peripheral surface and screwed onto the screw shaft, and the both screws Ends are fitted into holes formed in the outer peripheral portion of the nut so as to infinitely circulate a large number of balls loaded in a load area between the grooves so as to roll and the balls rolling in the load area. In a ball screw device provided with a substantially U-shaped ball circulation member,
From the ball scooping point where the ball is separated from the screw groove of the screw shaft to the ball circulation member side to the load region between the screw grooves, a buffer material that is more flexible than the material of the screw shaft is restrained by the ball on the nut side. A ball screw device characterized by being arranged on a surface.   The ball circulation member has leg portions fitted to the holes of the nut at both ends, and a passage for scooping up the ball and a return passage in each leg portion are inclined with respect to the outer peripheral surface of the leg portion. 2. The ball screw device according to claim 1, wherein a side cap made of a synthetic resin is formed, and a part of the leg portion is used as the cushioning material.

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